1. Field of the Invention
The present invention relates to a planar waveguide lens.
2. Description of the Prior Art
For many planar optical elements, lenses, embodied as a waveguide, are required. A representative example is an integrated optical spectrum analyzer, such as is described by D. B. Anderson et al in the IEEE, Journal of Quantum Electronics, QE-13 (1977), pp. 268-275. FIG. 1 illustrates such an integrated optical spectrum analyzer having two waveguide lenses. Here, the light coupled by a laser diode into the optical layer waveguide must be collimated with a first lens; the collimated light is then deflected through interaction with an acoustic surface wave, and, by means of a second lens (Fourier lens), again focused onto a detector row. A converter converts an applied a.c. voltage into the acoustic surface wave, which, in turn, is absorbed by an absorber. Since the deflection angle of the light is proportional to the frequency of the acoustic surface wave, the displacement of the focal spot on the detector row is likewise proportional to the acoustical frequency. The frequency analyzer, however, represents only one of many optical elements in which waveguide lenses are required.
Up to the present time, geodesic lenses (B. Chen and O. G. Ramer: IEEE, Journal of Quantum Electronics, QE-15 (1979), pp. 853-860), Luneberg lenses (F. Zernike: Opt. Commun. 12 (1974), pp. 379-381), and grid lenses (S. K. Yao and D. E. Thompson: Applied Physics Letters 33 (1978), pp. 635-637) have undergone testing as waveguide lenses. Although Luneberg lenses are relatively easy to manufacture, they are not suitable for substrates having a high refractive index, such as are frequently required. They therefore do not enter into consideration, for example for electrooptical substrates such as LiNbO.sub.3 or LiTaO.sub.3. Grid lenses and geodesic lenses are also suitable for highly-refractive substrates; however, in the case of grid lenses, strong imaging errors occur in the case of oblique incidence of light to the optical axis; geodesic lenses have the disadvantage that their reproducible manufacture and their accurate positioning relative to other components of the planar optical element (e.g. the detector row in the frequency analyzer) is very difficult.